Milkfish

Anatomy

The milkfish can grow to 1.80 m (5 ft 11 in), but are most often no more than 1 m (39 in) in length. They can reach a weight of about 14 kg (31 lb). and an age of 15 years. They have an elongated and almost compressed body, with a generally symmetrical and streamlined appearance, one dorsal fin, falcate pectoral fins and a sizable forked caudal fin. Mouth is small and toothless. Body color is olive green, with silvery flanks and dark bordered fins. They have 13-17 dorsal soft rays, 8-10 anal soft rays and 31 caudal fin rays.

Biology

These fishes generally feed on autotrophs, algae and small invertebrates. They tend to school around coasts and islands with coral reefs. The young fry live at sea for two to three weeks and then migrate during the juvenile stage to mangrove swamps, estuaries, and sometimes lakes, and return to sea to mature sexually and reproduce. Females spawn at night up to 5 million eggs in saline shallow waters.

Consumption

The milkfish is an important seafood in Southeast Asia and some Pacific Islands. Because milkfish is notorious for being much bonier than other food fish, deboned milkfish, called "boneless bangús" in the Philippines, has become popular in stores and markets. Despite the notoriety however, many people in the Philippines continue to enjoy the fish cooked regularly or even raw using kalamansi juice or vinegar to make kinilaw na bangus.

Popular presentations of milkfish in Indonesia include bandeng duri lunak (ikan bandeng is the Indonesian name for milkfish) from Central and East Java or bandeng presto which is pressure cooked milkfish until the bones are rendered tender, and bandeng asap or smoked milkfish. Either fresh or processed, milkfish is the popular seafood product of Indonesian fishing towns, such as Juwana near Semarang in Central Java, and Sidoarjo near Surabaya in East Java.

History

Milkfish aquaculture first occurred around 800 years ago in the Philippines and spread in Indonesia, Taiwan, and into the Pacific. Traditional milkfish aquaculture relied upon restocking ponds by collecting wild fry. This led to a wide range of variability in quality and quantity between seasons and regions.

In the late 1970s, farmers first successfully spawned breeding fish. However, they were hard to obtain and produced unreliable egg viability. In 1980, the first spontaneous spawning happened in sea cages. These eggs were found to be sufficient to generate a constant supply for farms.

Farming methods

Fry are raised in either sea cages, large saline ponds (Philippines), or concrete tanks (Indonesia, Taiwan). Milkfish reach sexual maturity at 1.5 kg (3.3 lb), which takes five years in floating sea cages, but eight to 10 years in ponds and tanks. Once they reach 6 kg (13 lb), (eight years), 3–4 million eggs are produced each breeding cycle. This is mainly done using natural environmental cues. However, attempts have been made using gonadotropin-releasing hormone analogue (GnRH-A) to induce spawning. Some still use the traditional wild stock method — capturing wild fry using nets. Milkfish hatcheries, like most hatcheries, contain a variety of cultures, for example, rotifers, green algae, and brine shrimp, as well as the target species. They can either be intensive or semi-intensive. Semi-intensive methods are more profitable at US$6.67 per thousand fry in 1998, compared with $27.40 for intensive methods. However, the experience required by labour for semi-intensive hatcheries is higher than intensive. Milkfish nurseries in Taiwan are highly commercial and have densities of about 2000/L. Indonesia achieves similar densities, but has more backyard-type nurseries. The Philippines has integrated nurseries with grow-out facilities and densities of about 1000/L. The three methods of outgrowing are pond culture, pen culture, and cage culture.

• Shallow ponds are found mainly in Indonesia and the Philippines. These are shallow (30–40 centimetres (12–16 in)), brackish ponds with benthic algae, usually used as feed. They are usually excavated from nipa or mangrove areas and produce about 800 kg/ha/yr. Deep ponds (2–3 m) have more stable environments and their use began in 1970. They so far have shown less susceptibility to disease than shallow ponds.
• In 1979, pen culture was introduced in Laguna de Bay, which had high primary production. This provided an excellent food source. Once this ran out, fertilizer was applied. They are susceptible to disease.
• Cage culture occurs in coastal bays. These consist of large cages suspended in open water. They rely largely on natural sources of food.

Most food is natural (known as lab-lab) or a combination of phytoplankton and macroalgae. Traditionally, this was made on site; food is now made commercially to order. Harvest occurs when the individuals are 20–40 cm long (250–500 g in weight). Partial harvests remove uniformly sized individuals with seine nets or gill nets. Total harvest removes all individuals and leads to a variety of sizes. Forced harvest happens when an environmental problem occurs, such as depleted oxygen due to algal blooms, and all stock is removed. Possible parasites include nematodes, copepods, protozoa, and helminths. Many of these are treatable with chemicals and antibiotics.

Processing and marketing

Traditional post-harvest processing include smoking, drying, and fermenting. Bottling, canning, and freezing are of recent origin. Demand has been steadily increasing since 1950. In 2005, 595,000 tonnes were harvested worth US$616 million.

A trend toward value-added products is occurring. In recent years, the possibility of using milkfish juveniles as bait for tuna long-lining has started to be investigated, opening up new markets for fry hatcheries.

Golden bangus

On April 21, 2012, a Filipino fisherman donated a milkfish with yellowish coloring to the Philippine Bureau of Fisheries and Aquatic Resources, which was later on called the "golden bangus". However, the fish soon died, allegedly because of a lower level of oxygen in the pond to which it was transferred.